From: Namhyung Kim <namhyung.kim@lge.com>
To: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, Paul Mackerras <paulus@samba.org>,
        Ingo Molnar <mingo@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
        Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [PATCH] perf top: Fix a race in callchain handling
References: <1336231388-12347-1-git-send-email-namhyung@gmail.com>
	<1336242167.2463.138.camel@laptop>
	<20120505235319.GB2150@infradead.org>
	<1336271107.1534.12.camel@leonhard>
	<20120506183212.GB2485@infradead.org>
	<878vh4srmh.fsf@sejong.aot.lge.com>
Date: Fri, 11 May 2012 11:10:59 +0900
In-Reply-To: <878vh4srmh.fsf@sejong.aot.lge.com> (Namhyung Kim's message of
	"Mon, 07 May 2012 10:32:22 +0900")
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Hi,

On Mon, 07 May 2012 10:32:22 +0900, Namhyung Kim wrote:
> On Sun, 6 May 2012 15:32:12 -0300, Arnaldo Carvalho de Melo wrote:
>> Em Sun, May 06, 2012 at 11:25:07AM +0900, Namhyung Kim escreveu:
>>> 2012-05-05 (토), 20:53 -0300, Arnaldo Carvalho de Melo:
>>> > I'm looking how to get that fixed with Peter concerns addressed.
>>> 
>>> I guess it's gonna be a non-trivial job. As far as I can see, the hists
>>> code can handle up to two concurrent threads regardless of the callchain
>>> cursor problem. And also guess that other areas of libperf also doesn't
>>> support the true concurrency, right?
>>
>> Right, but making it even less concurrent is something we should avoid
>> 8-)
>>
>> How about this one instead? At least we would be able to, concurrently,
>> process multiple, unrelated hists:
>
> I thought about it before, but it still cannot protect it from accessing
> a hists by multiple concurrent threads. IOW if two threads call the
> function to a same hists at the same time, ->callchain_collapse_cursor
> would still get the race problem - so crashed.
>
> I guess callchain_cursor should be thread-local, eventually. No need to
> make it hist-local IMHO.
>

So, any thoughts?

Thanks,
Namhyung
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